First you need to read this poorly titled sticky thread near the top of this forum: http://www.basenotes.net/threads/261...fumers-alcohol
That thread should really be titled "Everything you ever wanted to know about alcohol for perfumery".
It seems the situation in England is quite bad for obtaining pure 95% ethanol for perfumery. Here are my answers to your questions.
1. Some types of denatured alcohol have extremely small amounts of denaturant. You might search for something like that for sale in the UK. The problem is that every jurisdiction is different. Here in Canada I can get denatured 95% ethanol that has less than one part per million of Bitrex, also known as Denatonium. http://en.wikipedia.org/wiki/Denatonium. This is present in such minute quantities that honestly, if you did not know it was there, you would probably not have an allergic reaction. I'd suggest a double blind experiment where you obtain some alcohol denatured with Bitrex and some pure 95% ethanol and see if you can tell the difference (not drinking it but just spraying a fraction of a ml on your skin). In general, when I want to use a denatured alcohol for perfume, before I buy it, I simply ask the shopkeeper if I can put a drop on a piece of paper. Usually they are amenable to this. I then wait ten or twenty seconds and smell the paper. If I cannot smell anything, then I consider the stuff good for perfumery. Very often I *can* smell something, so that quickly ends the idea of buying that bottle of denatured alcohol. You can always try this with various brands available in the UK until you find one that works.
2. I have never heard of this tea tree idea. I would suggest however that by doing this, you are adding hundreds of different molecules to your alcohol, many of which will have distinctive smells that will perturb your perfumery results, and many of which might be sensitizing or allergenic, so it kind of defeats your purpose.
3. It appears that in the UK for the price of a few litres of that Rektyfikowany stuff you can probably buy the equipment you need to set up a small distillation apparatus and make your own pure ethanol from cheap wine or beer. Maybe start here: http://www.stillsmart.co.uk